External beam radiation therapy is one of the available non-invasive methods to treat a pathological anatomy (e.g., tumor, lesion, vascular malformation, nerve disorder, etc.). In one type of external beam radiation therapy, an external radiation source directs a sequence of x-ray beams at a target volume, e.g., a tumor, from multiple angles, with the patient positioned so the target volume is at the center of rotation (isocenter) of the beam. As the angle of the radiation source changes, every beam passes through the target volume, but passes through a different area of healthy tissue on its way to and from the target volume.
Image-guided radiation therapy (IGRT) systems include gantry-based systems and robotic-based systems. In gantry-based systems, the radiation source, e.g., a linear accelerator (LINAC), is mounted on a gantry that moves the source around a center of rotation (isocenter) in a single plane. The radiation source may be rigidly attached to the gantry or attached by a gimbaled mechanism. Each time a radiation beam is delivered to a target volume during treatment, the axis of the beam passes through the isocenter. Radiation beam delivery is, therefore, limited by the rotation range of the radiation source mounted on the gantry, the angular range of the gimbaled mechanism (if present), and by the number of degrees of freedom available on a patient positioning system. Additionally, the shape of the radiation can be modified using a multileaf collimator. Alternatively, the treatment system has the radiation source mounted on a robotic arm with at least five degrees of freedom to enable non-coplanar delivery to a target volume. One example of such a system is the CYBERKNIFE® Robotic Radiosurgery System manufactured by Accuray Incorporated. (Sunnyvale, Calif.).
One practical limitation for both gantry-based systems and robotic-based IGRT systems is space. Specifically, hospitals or other sites wishing to install such a system may have a specific room in which it is to be placed. However, the system may be too large for the room, thus requiring structural modification of the room. If the room cannot be modified within a specified budget (or at all), then it may be necessary to relocate the system; alternatively, the system's use may be entirely precluded at the site. Thus, it would be useful to reduce the size of an IGRT system. One way in which to do this is to reduce the amount of space required to generate the radiation beam (e.g., X-ray, electron, or proton beam).
One example of a prior art robot-based IGRT system 100 is illustrated in FIG. 1. System 100 includes robot-based support system 110, robot-based linear accelerator (LINAC) system 120, X-ray imaging sources 131, and detectors 132. Robot-based LINAC system 120 includes LINAC 121 and robotic arm 122. Robot-based support system 110 includes patient treatment couch 111, robotic arm 112, track 114, and column 115. Responsive to instructions from a controller (not shown), robot-based support system 110 moves robotic arm 112 in any suitable direction, e.g., along track 114 and/or column 115, so as to adjust the position and/or orientation of patient treatment couch 111 and thus appropriately position the patient before and/or during the radiation treatment, in accordance with a treatment plan. Also responsive to instructions from the controller, robot-based LINAC system 120 moves LINAC 121 to a desired position and orientation using robotic arm 122, and generates radiation of the desired type, energy, field, and dose using LINAC 121, again in accordance with the treatment plan. X-ray imaging sources 131 and detectors 132 are configured to obtain x-ray images of the patient or nearby anatomical structures responsive to instructions from the controller, e.g., at appropriate times before and during the radiation treatment. Each of x-ray imaging sources 131 is arranged at a predetermined angle relative to vertical, e.g., at 45° from vertical, such that x-ray radiation generated by that source passes through the target volume and is received by corresponding detector 132. Based on the received radiation, each of detectors 132 obtains an x-ray image of the target volume. The pair of thus-obtained images may be referred to as “stereoscopic x-ray images,” and is provided from detectors 132 to the controller for use in guiding irradiation of the patient with LINAC 121.
As is familiar to those skilled in the art, LINACs are designed to accelerate charged particles along a linear pathway. Generally, a LINAC includes a charged particle source, e.g., a source of electrons, protons, or ions, and an evacuated chamber along which the particles are accelerated. Depending on the type of charged particle, the evacuated chamber may be relatively long. For example, chambers for the acceleration of electrons may be between 0.5 and 1.5 meters long. Orienting such a chamber generally perpendicularly to the patient treatment couch, as is the case for LINAC 121 illustrated in FIG. 1, may substantially increase the overall height of the system. As such, the space requirements for installing and operating the system may increase correspondingly, thus potentially presenting practical problems for installing the system at space-constrained sites.